The Immersed Body Method and Its Use in Modelling Vertical Axis Turbines

Abstract

The focus of this thesis is on the development of a fluid–solid interaction (FSI) model, based on the idea of the immersed boundary method. The novelty of this approach is the combination of a two–fluid approach to represent the solid phase on a fluid finite–element mesh, with the conservative projection of data between two unrelated meshes. While this is an important feature for two–way coupled FSI models, this thesis analyses the outcome of this method based on one–way coupled FSI problems, in which the solid phase has a prescribed velocity. The presented FSI method is validated on several test cases with static solids as well as solids with a prescribed velocity. For complex computational fluid dynamic (CFD) problems, mesh adaptivity methods are used to reduce the computational effort while obtaining the same accuracy compared to fixed meshes. In this work mesh adaptivity is also used to increase the resolution of the fluid mesh near the solid boundary in order to obtain an accurate representation of the solid’s shape on the fluid mesh. However, spurious peaks in the pressure occur due to the projection of fields after adapting the mesh. This causes peaks in the drag force and results in a potential problem by decreasing the accuracy, especially for two–way coupled FSI problems. Since the FSI method was developed with two–way coupled FSI problems in mind, the occurrence of the spurious peaks was analysed and methods are shown to minimise the peaks in the drag force. Finally, the developed FSI method is applied to rotating vertical axis turbines and the results are compared to experimental results. This again shows the difficulties of applying the method and assesses how it can be used for turbine modelling, and furthermore used for analysing optimised turbine layouts.